Field
Embodiments of the invention generally relate to laser annealing systems with optics for imaging a pattern on a substrate. More specifically, embodiments of the invention relate to a customized pupil stop shape for control of edge profile in laser annealing systems.
Description of the Related Art
Thermal processing is commonly practiced in the semiconductor industry. Semiconductor substrates are subjected to thermal processing in the context of many transformations, including doping, activation, and annealing of gate, source, drain, and channel structures, siliciding, crystallization, oxidation, and the like. Techniques of thermal processing have progressed from simple furnace baking to various forms of increasingly rapid thermal processing such as RTP, spike annealing, and laser annealing.
Conventional laser annealing processes use laser emitters that may be semiconductor or solid state lasers with optics that focus, defocus, or variously image the laser light into a desired shape. A common approach is to image the laser light into a line or thin rectangular image. The laser light is scanned across a substrate (or the substrate is moved beneath the laser light) to process the surface of the substrate.
It is well known that the image produced with coherent light exhibits sharp definition, but also includes a pronounced overshoot, or “ringing” effect, characterized by high intensity non-uniformities near the edge of the image, while the same image produced with incoherent light exhibits less definition, characterized by a soft shoulder and somewhat broadened roll-off width, but also exhibits less overshoot. In the case of partially coherent light, the image produced has a reduced ringing effect when compared to an image produced with fully coherent light which exhibits a more narrow roll-off than an image produced with fully incoherent light. The ringing effect and roll-off may be affected by the use of an aperture in the laser optics system. However, current apertures generally do not provide desired results with respect to overshoot and roll-off.
Accordingly, there is a need in the art for improved apertures in laser annealing systems.